An expansion tank, which is able to equalize the fluctuations in volume caused by thermal expansion in the cooling system by varying the filling level, is normally provided as an expansion device at the highest point in a cooling system such as that currently commonly used in motor vehicles. Furthermore, the expansion tank proper normally neither contains nor is connected via a pipe to an expansion chamber which is able to take up or release liquid volumes during minor pressure fluctuations. Because of the latter, the normal pressure relief valve or vacuum valve is prevented from operating during normal operation, which is said to reduce the mechanical stress on the cooling system.
Moreover, the prior art cooling systems commonly used in motor vehicles are expensive. In particular, the mounting of the expansion tank especially commands high costs because it requires a holder in the motor vehicle and tubings must be installed. In addition, the expansion chamber also proposed in the above-mentioned DDR-PS No. 136,280 causes an additional increase in the cost of the cooling system. And the fact that the liquid level in the expansion tank is subject to considerable fluctuations, which makes monitoring of the filling level difficult, is functionally disadvantageous.